A Gas Insulated Switchgear (GIS) is used to control the supply of electrical power between a source, such as a transformer, and a load, such as a factory. A GIS is a distributing board that contains high or medium voltage electrical devices in a pressure-resistant tank filled with gas. In general, a GIS receives electrical power through a main bus and passes it through a circuit breaker unit, to a potential current transforming unit, a main bus-bar unit and to the load through cables. The circuit breaker monitors the supply and disconnects the main bus from the load if an abnormality is detected. A pair of switches is provided, one on either side of the circuit breaker to permit the circuit breaker to be isolated. To provide for continuity of power, a secondary feed is provided from a second or transfer bus. In one configuration, known as a transfer bus configuration, this bypasses the circuit breaker and supplies power directly to the current transformer. A switch is provided between the secondary bus and the current transformer so that supply from only one bus is permitted.
The power carrying components are located within a localized gas environment. This typically is SF6 gas which has excellent characteristics for insulating and arc extinction. These characteristics enable the components to be placed closer to one another than in an air insulated switch and therefore allow for substation miniaturization, improvement of safety and reliability, ease of operation and maintenance, and so on.
A conventional GIS contains the circuit breaker unit, a current transforming unit and a cable terminal in a single sealed container and shares insulating gas (i.e., SF6 gas). Therefore, if the circuit breaker of the conventional GIS requires service or inspection, it is necessary to interrupt the power supply and evacuate the insulating gas from the sealed container for maintenance or replacement of the circuit breaker unit. A related technology is disclosed in Korea patent No 10-0959521.
Where a continuity of power supply is provided, such as by a transfer bus, the switch and other components associated with the transfer bus may be designed to function safely as the circuit breaker is serviced. The absence of an insulating gas may therefore be compensated for by increased spacing of the components.